We are interested in the mechanisms by which RNA tumor viruses replicate and induce neoplastic transformation. The objectives of the proposed study include the elucidation of the biochemical nature of the oncornavirus 70S RNA genome and the mechanism of RNA-directed DNA synthesis by their DNA polymerases. More specifically, we will address the subunit nature of the 70S RNA by nucleotide sequence and hybridization studies in order to determine whether the high molecular weight subunit species are unique, with respect to one another, or whether they represent identical sets of genetic information (redundancy). Genomes of sarcoma and leukosis viruses will be compared to directly determine the extent of homology (genetic relatedness) between transforming and nontransforming viruses. Such studies will be extended to determine whether the processes of genetic reassortment (virus-virus genetic exchange) and/or recombination (virus-cell genetic exchange) occur during infection by RNA tumor viruses. Studies on RNA-directed DNA synthesis will include mechanisms of initiation of DNA synthesis, synthesis of double-stranded DNA, and extent of RNA-directed DNA transcription by the RNA tumor virus DNA polymerases.